1. Field of the Invention
The present invention relates to a junction flexible wiring circuit board used for performing junction between a suspension board for mounting a magnetic head of a hard disk drive thereon and a control circuit board for operating the magnetic head.
2. Related Art
As shown in FIG. 12, there has been heretofore known a hard disk drive having a magnetic head 1, a suspension board 2 for mounting the magnetic head 1 thereon, a control circuit board 3 for operating the magnetic head 1, and a junction flexible wiring circuit board 4 for performing junction between the suspension board 2 and the control circuit board 3.
The magnetic head 1 is supported on a front end portion of the suspension board 2 while separated by a small gap from a magnetic disk (not shown) rotating at a high speed, so that the magnetic head 1 keeps a good floating posture against the stream of air produced in the gap.
The suspension board 2 is constituted by a circuit-provided suspension board which includes predetermined wiring circuit patterns 7 integrally formed on a metal substrate 5. More specifically, an electrically insulating base layer 6 made of polyimide or the like is formed on the metal substrate 5 made of stainless steel foil or the like. Predetermined wiring circuit patterns 7 made of copper foil or the like are formed on the electrically insulating base layer 6. The wiring circuit patterns 7 are covered with an electrically insulating cover layer 8. A magnetic head side connection terminal portion 9 for connecting the magnetic head 1 is formed in a front end portion of the suspension board 2. The magnetic head 1 is mounted on the suspension board 2 so as to be connected to the magnetic head side connection terminal portion 9. A junction flexible wiring circuit board side connection terminal portion 10 for connecting a suspension board side connection terminal portion 14 of the junction flexible wiring circuit board 4 which will be described hereunder is formed in a rear end portion of the suspension board 2.
The junction flexible wiring circuit board 4 is formed as follows. An electric conductor layer 12 made of copper foil or the like is formed as predetermined wiring circuit patterns on an electrically insulating base layer 11 made of polyimide or the like, and the electric conductor layer 12 is covered with an electrically insulating cover layer 13. The suspension board side connection terminal portion 14 for connecting the junction flexible wiring circuit board side connection terminal portion 10 of the suspension board 2 is formed in the front end of the junction flexible wiring circuit board 4. A control circuit board side connection terminal portion 15 for connecting a connection terminal portion 16 of the control circuit board 3 is formed in a rear end portion of the junction flexible wiring circuit board 4. The suspension board side connection terminal portion 14 is connected to the junction flexible wiring circuit board side connection terminal portion 10 of the suspension board 2 while the control circuit board side connection terminal portion 15 is connected to the connection terminal portion 16 of the control circuit board 3.
The frequency of signal transmission becomes higher and faster data transmission has been advanced in recent years. Therefore, Matching of characteristic impedance has been required on the whole of a signal transmission path composed of the magnetic head 1, the suspension board 2, the junction flexible wiring circuit board 4, and the control circuit board 3 in the hard disk drive.
Matching of characteristic impedance was, however, generated between the junction flexible wiring circuit board 4 and the suspension board 2 because characteristic impedance of the junction flexible wiring circuit board 4 was higher than that of the suspension board 2. Hence, signal reflection occurred in a junction portion between the junction flexible wiring circuit board 4 and the suspension board 2 and caused deterioration of transmission characteristic.
Therefore, it might be conceived that the line width and space width of these wiring circuit patterns were adjusted suitably to obtain characteristic impedance matching between the suspension board 2 and the junction flexible wiring circuit board 4. In practice, the wiring circuit patterns, however, must be formed in a limited space. It was difficult to obtain characteristic impedance matching in the above-mentioned method.
The present invention is devised upon such circumstances and an object of the present invention is to provide a junction flexible wiring circuit board adapted for high-frequency signal transmission so that characteristic impedance matching is obtained in a signal transmission path of a hard disk drive, especially between a suspension board and the junction flexible wiring circuit board by a simple configuration.
In order to achieve the above object, according to the present invention, there is provided a junction flexible wiring circuit board used for performing junction between a suspension board for mounting a magnetic head of a hard disk drive thereon and a control circuit board for operating the magnetic head, wherein the junction flexible wiring circuit board is provided with a metal layer formed as a front surface layer of the junction flexible wiring circuit board.
Further, according the present invention, preferably, the junction flexible wiring circuit board has a plurality of wiring circuit patterns disposed at intervals of a predetermined distance, and the metal layer is formed at least in a position opposite to the wiring circuit patterns. Further, preferably, a width of each of the wiring circuit patterns is not projected out from a width of the metal layer.
Further, preferably, a width of the metal layer is formed to be not smaller than a sum of a total width of the wiring circuit patterns and a total width of intervals between the wiring circuit patterns, and a width of each of the wiring circuit patterns is not projected out from the width of the metal layer.
Further, preferably, each of the wiring circuit patterns has at least one write line and at least one read line; the metal layer has a write line side metal layer portion opposite to all of the write lines, and a read line side metal layer portion disposed at a predetermined distance from the write line side metal layer portion so as to be opposite to all of the read lines.
In this case, preferably, a width of the write line side metal layer portion is formed to be not smaller than a sum of a total width of the write lines and a total width of intervals between the write lines, a width of each of the write lines portion is not projected out from the width of the write line side metal layer portion, a width of the read line side metal layer portion is formed to be not smaller than a sum of a total width of the read lines and a total width of intervals between the read lines, and a width of each of the read lines is not projected out from a width of the read line side metal layer portion.